Soldering is a general technique for mounting electronic components on the surface of a printed circuit board. However, soldering produces corrosive flux residues that decrease the quality of the printed circuit substrate.
For this reason, soldering must be followed by a process for cleaning the substrate, so as to remove the residues.
Among various kinds of cleaners for removing flux residues, a cleaner obtained by adding a polyoxyalkylene phosphate-based surfactant to a halogen-free organic solvent formed of a polyoxyalkylene glycol ether-based compound is known by its reduced risk of ignition by flame, small influence on environment, and excellent property of dissolving flux residues (e.g., Patent Document 1 or 2).
However, the cleaning effect of this cleaner is not sufficient when the object to be cleaned is, for example, a mounted substrate having a complicated and precise structure. For example, when cleaning a FC or BGA printed circuit board in which the chip is bonded with the circuit using a large number of micro solder bumps, flux residues adhered on micrometer-level portions or in micrometer-level narrow gaps cannot be adequately removed by the above cleaner.
In view of this problem, for example, a related art document (Patent Document 3) discloses, a cleaner containing a polyoxyalkylene alkyl ether-based halogen-free organic solvent and an amine-based compound having a specific molecular weight. This cleaner is adjusted to have a specific viscosity range at 25° C.
However, when cleaning the substrate obtained by mounting the components onto the surface thereof using a lead-free solder, the above cleaner cannot adequately remove the flux residues adhered on narrow portions or in narrow gaps. In addition, the dirt removed in the cleaning process recontaminates the object to be cleaned during the water-rinsing process, leaving white residues on the board.
When the object to be cleaned is a sheet-type article, such as a mounted board, it is common to use a spray to apply the cleaner and the rinsing liquid (water, in general) to the object so as to improve efficiency during the cleaning process and water-rinsing process.
However, for example, when water is sprayed to the object after the object is cleaned using the cleaner of Patent Document 1 or 2, a large amount of foams are generated on the surface of the object. This causes some complications in the management of the water-rinsing process. An antifoaming agent may solve this problem; however, the use of an antifoaming agent may result in improper washing.
[Citation List]
    [Patent Document 1] Japanese Unexamined Patent Publication No. 1992-57899    [Patent Document 2] Japanese Unexamined Patent Publication No. 1996-73893    [Patent Document 3] Japanese Unexamined Patent Publication No. 1998-168488